A gas turbine engine may be used to power various types of vehicles and systems. A particular type of gas turbine engine that may be used to power aircraft is a turbofan gas turbine engine. A turbofan gas turbine engine conventionally includes, for example, five major sections: a fan section, a compressor section, a combustor section, a turbine section, and an exhaust section.
The fan section is typically positioned at the inlet section of the engine and includes a fan that induces air from the surrounding environment into the engine and that accelerates a portion of this air towards the compressor section. The remaining portion of air induced into the fan section is accelerated into and through a bypass plenum and out the exhaust section. The compressor section raises the pressure of the air to a relatively high level.
The compressed air from the compressor then enters the combustor section, where a plurality of fuel nozzles injects a steady stream of fuel into a combustion chamber formed by two liners joined by a dome. The combustor dome may be made of a double wall to provide protection from hot gases. The double walled dome typically has an inner surface, aligned towards the flame, that may be referred to as a heat shield. After the injected fuel is ignited in the combustor, the energy of the compressed air significantly increases. The high-energy compressed gases from the combustor section then flows into and through the turbine section, causing rotationally mounted turbine blades to rotate and expand these gases to produce mechanical energy. The gases exiting the turbine section is exhausted from the engine via the exhaust section, and the energy remaining in the exhaust gas aids the thrust generated by the air flowing through the bypass plenum.
Because combustors are subjected to high temperatures (e.g., temperatures in excess of 2000° C.), they may have limited service lives. In some cases, combustors may have high heat release rates. Thus, the liner, dome, or heat shield surfaces of the combustor may crack, oxidize, or become distorted. To improve the service life of the combustor, the temperature of the liner, dome, or heat shield may be lowered.
Multi-holed angled effusion cooling can be used to lower liner, dome, or heat shield temperatures. In this regard, a plurality of “effusion holes”, which are formed through the combustor liner, direct cooling air from outside of the combustor liner to an inner surface of the combustor liner (e.g., where the combustor liner is exposed to the high temperatures). As a result, the liner is cooled as air flows through each effusion hole and enters the combustor to form an air film to thereby isolate the high temperature gases from the liner. To enhance effusion film cooling effectiveness, the area and shape of effusion holes may be varied from a smaller circular inlet to a larger, fan shaped outlet. Varying the area of the effusion holes may cause the air to diffuse so that its velocity is reduced as the air film forms.
In the alternative to or in addition to effusion cooling, impingement cooling can be used to lower liner, dome, or heat shield temperatures. Impingement cooling works by blowing onto the inner surface of the combustor with high velocity air. This allows more heat to be transferred by convection than regular convection cooling does.
Traditional approaches to impingement and effusion cooling separate the impingement holes from the film cooling (effusion) holes. This separation is desired because of the manufacturing techniques that preclude (or largely inhibit) non line-of-sight holes. The separation of the impingement and effusion cooling also inhibits heat transfer between the liner providing the impingement cooling and the liner providing the effusion cooling, leading to thermally decoupled mechanisms that require compliant or slip joints to accommodate the thermal expansion differences between the liners. By combining the film and impingement in one liner, this affords the opportunity to eliminate compliant or slip joints and optimizes heat transfer. In addition, the opportunity for combining impingement and film/effusion cooling into one liner can provide cost/weight benefits relative to these approaches.
Accordingly, it is desirable to provide for an impingement-effusion cooling configuration that exhibits improved cooling effectiveness. Additionally, it is desirable to provide such configurations at a reduced manufacturing cost and at a reduced overall weight as compared to prior art combustors. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.